Chromophores of chromophores: a bottom-up Hückel picture of the excited states of photoactive proteins

Abstract

Citation for published item:enst¤ oterD gte F nd henD ghrlie F nd erletD tn F F @PHIUA 9ghromophores of hromophores X ottomEup r¤ ukel piture of the exited sttes of phototive proteinsF9D hysil hemistry hemil physisFD IW @RRAF ppF PWUUPEPWUUWF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Here, we present a reductionist approach to gain fundamental insight into the evolution of electronic structure as the chromophore increases in complexity from phenolate to that in GFP. Using frequency-and angle-resolved photoelectron spectroscopy, in combination with electronic structure theory, the onset of excited states that are responsible for the characteristic spectroscopic features in biochromophores are determined. A comprehensive, yet intuitive picture of the effect of phenolate functionalisation is developed based on simple Hückel theory. Specifically, the first two bright excited states can be constructed from a linear combination of molecular orbitals localised on the phenolate and para-substituent groups. This essential interaction is first observed for p-vinyl-phenolate. This bottom-up approach offers a readily accessible framework for the design of photoactive chromophores.

Photoelectron Imaging and Quantum Chemistry Study of Phenolate, Difluorophenolate, and Dimethoxyphenolate Anions

“…12 This previous study found that ezDyson predicted a smaller β 2 parameter (a more isotropic angular distribution) than was observed experimentally for the direct detachment feature at wavelengths longer than 370 nm. At wavelengths shorter than 370 nm, the overlapping feature arising from autodetachment from the S 1 state led to a decrease in the β 2 parameter, leading to values which appear more in agreement with ezDyson predictions at 12,[14][15][16][17] Good agreement was also found between the experimentally determined onset of the S 1 (1ππ * ) state (∼369 nm) and previous photoelectron spectroscopy measurements; 12 however, the higher resolution of the photoelectron spectra presented here has allowed us to locate a second bright resonance with AEE ∼ 335 nm. The experimentally determined average value of β 2 deviates from the trend predicted by ezDyson in the wavelength range where the direct detachment feature is overlapped in eKE with the resonant autodetachment feature, in agreement with the previous observations.…”

“…1, R=F and R=OMe, respectively) have been shown to become fluorescent when bound to specific ribonucleic acid (RNA) sequences. 9,10 It has been proposed that the electronic structure of the deprotonated GFP chromophore anion is governed by the phenolate molecular unit, 11,12 so our understanding of the electronic structure of the difluoro-and dimethoxy-substituted analogues will benefit from a detailed understanding of the electronic structure of the difluoroand dimethoxy-substituted phenolate building blocks. Experimentally, a direct way of probing the electronic structure of molecules is to use photoelectron spectroscopy.…”

“…UV photoelectron spectroscopy studies of the phenolate anion have been reported by several groups. 12,[14][15][16][17] An accurate value for the S 0 −D 0 adiabatic detachment energy (ADE) has been determined using slow-electron velocity-map imaging (SEVI) (2.2532±0.0004 eV) 16 and the vibrational envelope of the S 0 −D 0 transition has been found to be dominated by a progression in the v 11 ring stretching mode. [14][15][16][17] Direct detachment to D 0 has been observed to generate photoelectrons with perpendicular PADs, as expected for photodetachment from an orbital with π character, and become increasingly anisotropic with increasing photoelectron kinetic energy above the S 0 −D 0 threshold.…”

“…However, the measured PADs were found to become more isotropic with decreasing wavelength when λ ≤ 370 nm which was attributed to the onset of the S 0 → S 1 electronic transition at λ ∼ 370 nm, and rationalised by assuming that autodetachment from the S 1 state generates photoelectrons with an isotropic or parallel angular distribution that effectively cancels out the perpendicular anisotropy of the direct detachment contribution to the photoelectron spectrum. 12…”

Evidence of Electron Capture of an Outgoing Photoelectron Wave by a Nonvalence State in (C6F6)n–

“…The non-valence state of C6F6 − has the nuclear geometry of that of the S0 state owing to the very weak interaction of the diffuse orbital with the neutral core. 10,14 While there are clear signatures of dynamics involving resonances in the 2D-PE spectra (feature (iv) in Figure 1(a)), 22,[24][25][26] there is no apparent evidence for the formation of the non-valence state of C6F6 − . 14 This is of course not surprising given that the Franck-Condon overlap between anion and the neutral ground states is poor.…”